diffutils: The GNU collection of diff utilities1

You can use the 'diff' command to show differences between two
files, or each corresponding file in two directories.

You can use the 'cmp' command to show the offsets and line numbers
where two files differ. 'cmp' can also show all the characters that
differ between the two files, side by side.

You can use the set of differences produced by 'diff' to distribute
updates to text files (such as program source code) to other people.
This method is especially useful when the differences are small compared
to the complete files.

You can use the 'diff3' command to show differences among three
files. When two people have made independent changes to a common
original, 'diff3' can report the differences between the original and
the two changed versions, and can produce a merged file that contains
both persons' changes together with warnings about conflicts.